html,
body,
.box,
.chart
{
    width:100%;
    height: 100%;
}
.box{
    position: relative;
}
.backBtn{
    position: absolute;
    top:40px;
    left:40px;
    width:100px;
    height: 36px;
    line-height:34px;
    color:#666;
    border-radius: 6px;
    box-shadow: 0 0 10px #ccc;
    cursor: pointer;
    z-index: 1000;
}